The present disclosure relates to bidirectional couplers, monitor circuits, and front end circuits.
To date, directional couplers that process a plurality of high-frequency signals different in frequency band have been known (see for example, Japanese Unexamined Patent Application Publication No. 2002-100909).
FIG. 18 is a perspective view that illustrates an example of a configuration of the directional coupler disclosed in Japanese Unexamined Patent Application Publication No. 2002-100909. The names of the constituent elements and the references used hereinafter may be different from those in Japanese Unexamined Patent Application Publication No. 2002-100909 for convenience of explanation.
The directional coupler 9 in FIG. 18 includes a first main line 91, a second main line 92, a first sub line 93, a second sub line 94, and a ground 96.
The first main line 91 and the second main line 92 are arranged with the ground 96 interposed therebetween. The first sub line 93 and the second sub line 94 are arranged with the ground 96 interposed therebetween and are coupled to the first main line 91 and the second main line 92, respectively. The first sub line 93 and the second sub line 94 form a single sub line 95 by their respective one ends being connected.
One end and the other end of the first main line 91 constitute an input port P1 and an output port P2 while one end and the other end of the second main line 92 constitute an input port P3 and an output port P4. One end and the other end of the sub line 95 constitute a coupling port P5 and an isolation port P6.
For example, the directional coupler 9 is provided in a mobile phone terminal adaptable to a dual band, where two transmission signals different in frequency band are processed and is used so as to monitor intensities of the transmission signals.
Specifically, one and the other of the two transmission signals are supplied to the input ports P1 and P3, respectively, and propagate through the first main line 91 and the second main line 92 to be supplied to an antenna from the output ports P2 and P4. A first monitor signal corresponding to the intensities of the transmission signals is extracted from the coupling port P5. The first monitor signal is used for feedback control of transmission electric power for example.